The construction of these tires is characterised by the fact that they comprise rubber profiled elements of great thickness arranged in the sidewalls, and generally placed between the inner liner and the carcass reinforcement ply (plies). The function of these products is to bear the load when the pressure of the air in the tire is no longer such as to be able to perform this function.
Due to this arrangement, the construction of this type of tire requires particular arrangements to provide a correct join between the different profiled elements, and all the arrangements must be made so as to avoid trapping air between the different profiled elements, in particular when a cylindrical drum is used.
This is because, when laying the profiled elements of great thickness at the axial location corresponding to the zone of the sidewalls, it is observed that the meridian profile acting as a receiving surface for the carcass reinforcement ply is relatively distorted. The effect of this is to promote air becoming trapped between the carcass reinforcement ply and the profiled elements located radially below.
One solution which makes it possible to solve this problem was proposed in publication EP 634 266.
Grooves are arranged on the receiving surface of the drum, and are spaced axially apart so as to be positioned substantially below the zone of laying the profiled elements of great thickness. In this manner, by appropriately determining the shape of the groove, it becomes possible to obtain a substantially cylindrical laying surface for the carcass reinforcement ply. The profiled element of great thickness closely follows the profile of said groove such that its radially outer surface is substantially aligned with the generally cylindrical outer surface of the assembly drum.
Still in accordance with the publication EP 634 266, and when an assembly drum of variable diameter is used, the groove may contain circumferentially arranged membranes or elastic bodies. The shape of the membrane or the elastic body is adapted to impart to the drum a generally cylindrical external profile when the drum is positioned at its first laying diameter and said membrane is inflated or the elastic body is not subjected to any elastic stress. This particular arrangement makes it possible to fill the depression formed by the groove when the inner liner and the profiled element of great thickness are laid, and makes it possible to lay said profiled elements on a drum having a generally cylindrical shape.
The following profiled elements are generally laid once the drum has been moved to a second laying diameter. During this operation, the membrane or the elastic body is compressed under the effect of the elastic forces and is flattened against the bottom of the groove. The profiled element of great thickness and the inner liner then lie closely against the new profile of the groove.
Things are arranged so that, at the end of this first shaping, the radially outer surface of the profiled element of great thickness is aligned with the laying surface of the drum to form a receiving surface which is again generally cylindrical, so that the carcass reinforcement ply can then be laid on a surface devoid of zones liable to trap air.
The assembly operations can then be continued entirely conventionally in a manner known to the person skilled in the art, which consists of depositing for example the heel filling rubber and the heel reinforcement rings, then expanding the drum a second time up to a third laying diameter so as to anchor the heel reinforcement rings, and to permit the upturn of the ends of the carcass reinforcement ply to be turned up around the heel reinforcement rings.
However, developing the membranes or the elastic bodies has proved particularly difficult in obtaining a stable laying surface when the drum is positioned at the first laying diameter. This is because it is observed that the effect of the laying tension of the profiled element of great thickness being applied to the receiving surface located axially in line with the elastic body is to compress said elastic body and to modify substantially the laying diameter.
Furthermore, when it is desired to obtain a groove having a specific meridian profile, matched to the transverse profile of the profiled element of great thickness or alternatively when it is desired to modify the axial distance between the heel reinforcement rings it is necessary to make dimensional adaptations which require accurate adjustment of the aforementioned elastic restoring forces and hence of the materials used for producing the elastic bodies.